[Qemu-devel] [RFC 07/13] block: add thread_aio_context TLS variable

[Stefan Hajnoczi <stefanha@redhat.com>]

BH and fd handler APIs need to know which AioContext (event loop) to run
inside.  Passing it around everywhere is not feasible since it would
require adding arguments to any call-chain that invokes BH and fd
handler APIs (hint: there are many and they change).

Instead make the AioContext pointer thread-local.  This way, any
function that needs to use an AioContext can find it.  In particular:
the iothread and vcpu threads share the main AioContext since they hold
the global mutex while running.  Dataplane threads will use their own
AioContexts.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 async.c             | 2 ++
 cpus.c              | 2 ++
 include/block/aio.h | 4 ++++
 main-loop.c         | 1 +
 4 files changed, 9 insertions(+)

diff --git a/async.c b/async.c
index 90fe906..765cbc0 100644
--- a/async.c
+++ b/async.c
@@ -27,6 +27,8 @@
 #include "block/thread-pool.h"
 #include "qemu/main-loop.h"
 
+DEFINE_TLS(AioContext*, thread_aio_context);
+
 /***********************************************************/
 /* bottom halves (can be seen as timers which expire ASAP) */
 
diff --git a/cpus.c b/cpus.c
index c232265..529d612 100644
--- a/cpus.c
+++ b/cpus.c
@@ -741,6 +741,7 @@ static void *qemu_kvm_cpu_thread_fn(void *arg)
     qemu_thread_get_self(cpu->thread);
     cpu->thread_id = qemu_get_thread_id();
     cpu_single_env = env;
+    *alloc_thread_aio_context() = qemu_get_aio_context();
 
     r = kvm_init_vcpu(cpu);
     if (r < 0) {
@@ -815,6 +816,7 @@ static void tcg_exec_all(void);
 static void tcg_signal_cpu_creation(CPUState *cpu, void *data)
 {
     cpu->thread_id = qemu_get_thread_id();
+    *alloc_thread_aio_context() = qemu_get_aio_context();
     cpu->created = true;
 }
 
diff --git a/include/block/aio.h b/include/block/aio.h
index 1836793..6ee9369 100644
--- a/include/block/aio.h
+++ b/include/block/aio.h
@@ -17,6 +17,7 @@
 #include "qemu-common.h"
 #include "qemu/queue.h"
 #include "qemu/event_notifier.h"
+#include "qemu/tls.h"
 
 typedef struct BlockDriverAIOCB BlockDriverAIOCB;
 typedef void BlockDriverCompletionFunc(void *opaque, int ret);
@@ -74,6 +75,9 @@ typedef struct AioContext {
 /* Returns 1 if there are still outstanding AIO requests; 0 otherwise */
 typedef int (AioFlushEventNotifierHandler)(EventNotifier *e);
 
+/* Each thread can have a default AioContext */
+DECLARE_TLS(AioContext*, thread_aio_context);
+
 /**
  * aio_context_new: Allocate a new AioContext.
  *
diff --git a/main-loop.c b/main-loop.c
index cf36645..51eeb0f 100644
--- a/main-loop.c
+++ b/main-loop.c
@@ -142,6 +142,7 @@ int qemu_init_main_loop(void)
 
     gpollfds = g_array_new(FALSE, FALSE, sizeof(GPollFD));
     qemu_aio_context = aio_context_new();
+    *get_thread_aio_context() = qemu_aio_context;
     src = aio_get_g_source(qemu_aio_context);
     g_source_attach(src, NULL);
     g_source_unref(src);
-- 
1.8.1.4